1. Field of the Invention
The invention relates in general to a wireless transmission technique, and more particularly, to a technique for determining a packet output rate according to a time stamp.
2. Description of the Related Art
With advancements in communication techniques, digital television broadcasting gradually matures with time. The digital video broadcasting-second generation terrestrial (DVB-T2) is a very prevalent standard in digital television broadcastings. The DVB-T2 includes three video encoding methods—MPEG-2, H.264/MPEG-4 AVC, and AVS (Audio Video Standard). FIG. 1 shows a schematic diagram of a relationship between DVB-T2 wireless transmitter and receiver adopting the MPEG-2 standard.
A transmitter 10 comprises an encoder 12 and a modulator 14. A receiver 20 comprises a decoder 22, a demodulator 24, and a buffer 24. In this example, the encoder 12 encodes data corresponding to three different program channels to respectively generate three transport streams TS0, TS1, and TS2, each containing multiple packets. As shown in FIG. 1, the modulator 14 divides the transport streams into data streams data_PLP0, data_PLP1, data_PLP2, and common_PLP. The data stream common_PLP consists of common data packets of the transport streams TS0, TS1, and TS2. The data streams data_PLP0, data_PLP1, and dataPLP2 respectively comprise data packets excluding common data packets and null packets of the transport streams TS0 to TS2. By arranging the common packets in the data stream common_PLP, bandwidth consumed for repeatedly transmitting the same packets can be saved.
To assist the receiver 20 in correctly restoring the transport streams, the transmitter 10 selectively adds an input stream time reference (ISCR) to every packet or certain packets when generating the data packets. In practice, the modulator 14 may further include a counter. Each time a packet transmitted from the encoder 12 is received, the modulator 14 writes a current count of the counter to the ISCR of the packet.
Assuming a user at the receiver 20 selects to watch a program channel corresponding to the transport stream TS0, the demodulator 24 combines the data streams data_PLP0 and the common_PLP to generate a restored transport stream TS0′, which is then decoded by the decoder 22. As shown in FIG. 1, demodulated data packets are first stored in the buffer 26 before being forwarded to the decoder 22. In order to correctly reconstruct the transport stream TS0′, it is necessary that the receiver 20 first determine a bit rate for reading the packets from the buffer 26 according to the ISCR recorded in the packets.